Carbon brushes



July 24, 1962 J MILLET 3,046,425

CARBON BRUSHES Filed April 21, 1959 3 4 5 7 d/ I z Q Fi g2. Fi 3ngenllllr Z/ ZM A tlorn e United States Patent 3,046,425 CARBON BRUSHESJacques Millet, Paris, France, assignor to Societe le Carbone-Lorraine,Paris, France, a company of France Filed Apr. 21, 1959, Ser. No. 807,881Claims priority, application France Apr. 29, 1958 4 Claims. (Cl.310-228) The present invention relates to carbon brushes and has for anobject improvement therein.

A great number of compounds have already been proposed for brushesintended for use in electrotechnology, functioning in a rarefied and dryatmosphere. In order to improve the life and the behavior of the brushesat a high altitude, mineral or organic substances are generallyintroduced, these substances being dispersed in their mass or insertedunder various forms in the graphite block or which are joined to thelatter by various means.

It has already been proposed to incorporate sulphides, having acrystalline form which is very similar to that of graphite, in recesses,channels, grooves, etc. provided in the brushes. The sulphides used arepreferably finely powdered molybdenum sulphides which crystalliseaccording to the cubic or hexagonal system.

Brushes containing tin sulphide have proved more satisfactory than thosecontaining molybdenum sulphide because under vacuum they have a moreregular contact voltage.

However it has been found that brushes containing tin sulphidedistributed as referred to tend to leave on the collector traces ofsulphide which becomes deposited along the tracks of the channels.

It is a more specific object of this invention to remedy this drawback,to improve the operation of the brushes under vacuum or in a rarefiedatmosphere, and to avoid making scratches on the patina of the collectorand to stabilise the contact voltage.

Accordingly, the invention provides a carbon brush for use at highaltitudes or in a rarefied atmosphere, characterised by the introductionof a mixture of tin sulphide and a binding agent in channels or otherreceptacles arranged in said brush.

In the prior proposal referred to above, the sulphide is incorporatedwhilst maintaining the crystalline form of the sulphide, which will notbe modified either by baking or sintering.

According to a first specific embodiment of the present invention, thebinding agent may be a highly conductive metal having a low meltingpoint, such as a silver powder for example.

Silver powder has moreover the property that it starts to sinter in thecold. By compressing a powder mixture comprising approximately from 5 to15% of a silver powder, and of tin sulphide, a relatively solid metallicmass is obtained.

According to a first embodiment, a number of channels, pockets or otherreceptacles are formed in a block of graphite forming a brush. Thesereceptacles are then filled with a mixture comprising 90% tin sulphidehaving a given granulation and silver powder which is the binding agent.The mixture is vigorously compressed without sintering the tin sulphideand a brush is obtained, which operates satisfactorily. Brushes made insuch a manner have a coefficient of friction of 0.20 and their wear isvery much reduced. The wear, measured under vacuum, with a speed ofrotation of the brush against a contacting surface of 10 metres persecond, is lower than 0.17 mm. per hour. These same brushes show aconstant voltage drop on contact, said voltage drop being approximately0.75 volt. Comparative tests made with brushes which only comprise tinsulphide which is 3,046,425 Patented July 24, 1962 "ice not strengthenedby silver powder show under the same conditions a wear of 2.3 mm. perhour.

According to a second embodiment the binding agent consists of a styrenepolyester resin.

This resin has in particular the remarkable property of assisting in theformation and maintenance of a patina on the collectors. It lowers thecoefficient of friction and considerably improves the switchingproperties and the resistance to Wear of the brushes in a rarefiedatmosphere.

According to this second embodiment, a mixture of tin sulphide and 10%resin is introduced in the recesses, grooves, channels or otherreceptacles provided in the mass of the brushes. The polymerization ofthe resin may be effected in the presence of a hardening agent such abenzoyl peroxide for example. In this case heat is applied, duringpolymerisation. It may also be effected in the cold by adding anaccelerator such as cobalt naphthenate or methylethyl ketone peroxide.The tin sulphide is mixed with the resin before the latter hardens andthen the thus constituted paste is introduced in the receptacle. In situpolymerisation is effected under the above described conditions in thecold or with application of heat.

The voltage drop on contact measured on brushes made according to thissecond embodiment, as well as the lessening of wear, are of the sameorder of magnitude as in the case of the brushes manufactured accordingto the first embodiment.

The various specific embodiments of the invention may be illustrated byWay of non-limiting indication by means of the accompanying dravw'ngs.All these modifications cause the tin disulphide to sweep the greatestpossible width of the track in order to render the patina morehomogeneous.

FIGURE l'shows a graphitebrush 1, in which three deep pits or pockets 2have been bored. These pits or pockets may be filled either with amixture of tin sulphide and silver, or with a mixture of tin sulphideand styrene polyester resin. The number of receptacles 2, is notlimited. Moreover they may be in alignment or staggered.

FIGUREZ shows a cross-section of a brush 3 in which three series ofreceptacles have been made in staggered disposition, filled, as desired,with one or the other mixture.

FIGURES 3 and 4 show cross-sections of brushes 5 and 6 respectively inwhich the tin sulphide mixture is located in deep slots 7 and 8respectively, which are parallel to the largest side of thecross-section.

FIGURES 5 and 6 show cross-sections of brushes 9 and 10 respectively inwhich the tin sulphide mixture is located in slots 11 and 12respectively made along the diagonal of the cross-section or alongoblique and parallel slots.

The introduction of the sulphide-binder mixture may be efiected withvarious qualities of carbons and graphites. The form, the number, thearrangement and the direction of the recesses, grooves, channels or pitsand so on filled with the mixtures described in the present inventionmay vary in accordance with the particular application envisaged.

I claim:

1. A carbon brush for use at high altitudes and under rarefiedatmospheres containing at least one receptacle, and a mixture of tinsulphide and a binding agent in said at least one receptacle, saidbinder not being capable of modifying the structure of the tin sulphide.

2. A carbon brush for use at high altitudes and under rarefiedatmospheres containing at least one receptacle, and a mixture of tinsulphide and a styrene polyester resin in said at least one receptacle.

3 4 3. A carbon brush for use at high altitudes and under and a mixtureof 90% of tin sulphide and 10% of a styrarefied atmospheres containingat least one receptacle, rene polyester resin in said at least onereceptacle.

and a mixture of 90% of tin sulphide and 10% of a bind- References Citedin the file of this patent ing agent in said at least one receptacle,sa1d blnder not being capable of modifying the structure of the tin sul-5 UNITED STATES PATENTS p 2,736,830 Savage Feb. 28, 1956 4. A carbonbrush for use at high altitudes and under 2,730,743 El F b 5 1957rarefied atmospheres containing at least one receptacle, 2,909,452 Pa riOct 20, 1959

1. A CARBON BRUSH FOR USE AT HIGH ALTITUDES AND UNDER RAREFIEDATMOSPHERES CONTAINING AT LEAST ONE RECEPTACLE, AND A MIXTURE OF TINSULPHIDE AND A BINDING AGENT IN SAID AT LEAST ONE RECEPTACLE, SAIDBINDER NOT BEING CAPABLE OF MODIFYING THE STRUCTURE OF THE TIN SULPHIDE.